Primobolan is ,by far, the "safest" steroid. It has minimal affect on HPTA, is not 17-aa in any form, and has the mildest side effects.
It is also one of the best steroids to use for "keepable" gains. Gains made from this drug are as close to permanent as you are going to get, even with little to no PCT.
The major drawback to this drug is $$$. It costs a ton to run this drug in the proper dosages/cycle times. It is also a DHT derivative, so it will accelerate hair loss in those that are already genetically predisposed.
If you have access to this drug I can tell you from personal experience that a cycle of 750-1000mg test/wk and 600 mg/Primo will almost work miracles. For those not wanting heavy androgen use I have seen great gains from this one with little or no test as well.
Hope that helps.